The present invention relates generally to a method and apparatus for servicing air-conditioning systems and, more particularly, to a method and apparatus for testing, diagnosing, and repairing automotive air-conditioning systems.
It is estimated that more than 85 million passenger cars currently on the road in the United States are equipped with air-conditioning systems. In addition, trucks, vans, motor homes, and other vehicles are air-conditioned.
Several air-conditioner "service units" are available to assist a mechanic in servicing these vast numbers of air-conditioning systems, and one such service unit is described in commonly assigned U.S. Pat. No. 3,873,289. This unit is adapted to be connected to the high- and low-pressure sides of an automotive air-conditioning system and includes apparatus for measuring the high and low side pressures of the system, for draining and evacuating the system and for charging the system with refrigerant and lubricating oil.
When servicing an air-conditioning system with a service unit such as described in U.S. Pat. No. 3,873,289, the high and low side pressures of the system are first measured under appropriate operating conditions. These measured values are then compared with known standards for the particular air-conditioning system being tested; and from this comparison and other observable characteristics of the system, the mechanic decides whether or not the system is operating properly. If a system malfunction is indicated, the mechanic also determines the possible causes of the malfunction and decides how the system should be repaired. Depending on the type of repairs to be made, the service unit may then be used to either drain or evacuate the system or both drain and evacuate the system, to add to the system either refrigerant or lubricating oil, or both refrigerant and oil, as needed.
When using prior service units, the determination of whether or not an air-conditioning system is operating properly, the diagnosis of the possible causes of an improperly operating system, and the corrections needed to repair the system are essentially all made by a mechanic. Thus, accurate diagnosis and repair require that the mechanic possess substantial expertise. Many mechanics, however, service air-conditioning systems only occasionally as one aspect of providing general automotive repair services and do not have sufficient experience in servicing the various types of air-conditioning systems to be able to consistently service the systems in the most effective manner. Accordingly, with prior service units, misdiagnosis can frequently occur, resulting in improperly repaired systems and in excessive time consumption to complete the repairs.
Although service manuals are available to assist the mechanic in diagnosing and repairing air-conditioning systems, their use is time-consuming and inefficient. They also occupy valuable space and must be kept up to date.
Another inadequacy of many prior service units is that when using the unit to charge an air-conditioning system with oil, the mechanic must take special care to ensure that the system is properly charged because an improperly charged system will not operate satisfactorily. In some systems, it is necessary for the mechanic to adjust the charging time to compensate for variations in the viscosity of the oil due to variations in the oil temperature. In other systems, the weight of the oil source must be monitored by a digital scale or the like to ensure a proper charge.
In general, although prior service units provided the important advantage of placing much of the equipment needed to service an automotive air-conditioning system together in one cabinet, the basic steps of testing, diagnosing, and repairing the air-conditioning system still had to be performed by the mechanic.